Hastening Orientation Sensitivity

1. #262 #262 Hastening Orientation Sensitivity Nestor Matthews, Kei Kurosawa& Kristen Strong Department of Psychology, Denison University, Granville OH 43023 USA Results Introduction Discussion Training significantly hastened fine orientation sensitivity; temporal resolution improved by 51% at the cardinal axis, and 86% at the oblique axis. The training also sharpened angular resolution significantly at each axis. This sharpening was specific to the trained axis for each group. Why did cardinal learning occur? Here are two possibilities. Perceptual learning on a variety of visual tasks tends to be greater when external noise is added3. Studies using external noise4,5 suggest greater internal noise along oblique axes, which may explain why greater learning occurs at oblique axes. Here, rather than adding external noise, we exploited the imprecision that occurs naturally at extremely brief durations6,7. An alternate explanation for the present data is that the participants learned to ignore specific orientation bands within the mask. Mask-inhibition effects have been observed previuosly8 and would effectively “extend” the stimulus duration, thereby generating greater precision7. Previous studies1,2 showed that the ability to see subtle angular differences can improve with practice at oblique but not cardinal axes. The cause of this anisotropy is uncertain, and it is not known whether the same anisotropy pertains to temporal resolution –the briefest stimulus duration needed to achieve a specified angular resolution. Here, we used visual masks to investigate the extent to which fine orientation sensitivity could be both hastened and sharpened, at cardinal and oblique axes. Pre-training Hastening Method Pre / Post Training- The stimuli were sequentially presented gratings that were preceded and followed by a bulls-eye mask (as shown below). Participants judged whether the second grating in each pair was clockwise or anti-clockwise to the first. The stimulus duration across all 1,000 trials was 200 msec, and the angular difference ranged from -12 to 12 degrees. Cardinal-axis (horizontal) trials were blocked separately from oblique-axis (diagonal) trails. At each axis, 84% angular thresholds were computed for each participant. Participants were then split into two statistically indistinguishable groups for training. Training- During training each participant practiced at only one axis. Stimuli were presented at varying durations (8-158 msec) and the angular difference was equal to twice the pre-training 84% threshold. There were 10 blocks of 70 trials in each daily session. Each participant completed 5 days of training. Sharpening Specificity The Bottom Line The visual system’s response to subtle angular differences can be both hastened and sharpened, at cardinal and oblique axes. Sufficient initial levels of neural imprecision by be necessary for perceptual learning to occur. References Vogels & Orban (1985) PMID 3832592. Matthews & Welch (1997) PMID 9038408. Fine & Jacobs (2002) PMID 12678592. Heeley et al. (1997) PMID 9068823. Dakin, Mareschal & Bex (2005) PMID 16441191. Ringach, Hawken & Shapley (1997) PMID 9153392. Matthews, Rojewski & Cox (2005) PMID 15929646. Karni & Sagi (1991) PMID 2052578. This work can be viewed and downloaded at http://www.denison.edu/~matthewsn/vss2006.html and the Journal of Vision (in press)